EclipseLink expressions enable you to specify query search criteria based on the object model. EclipseLink translates the resulting query into SQL and converts the results of the query into objects. EclipseLink provides two public classes to support expression:

EclipseLink expressions enable you to specify query search criteria based on the object model. EclipseLink translates the resulting query into SQL and converts the results of the query into objects. EclipseLink provides two public classes to support expression:

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* The org.eclipse.persistence.Expression class represents an expression, which can be anything from a

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* The org.eclipse.persistence.expressions.Expression class represents an expression, which can be anything from a

simple constant to a complex clause with boolean logic. The developer can manipulate, group, and integrate expressions in several ways.

simple constant to a complex clause with boolean logic. The developer can manipulate, group, and integrate expressions in several ways.

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* The org.eclipse.persistence.ExpressionBuilder class is the factory for constructing new expressions.

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* The org.eclipse.persistence.expressions.ExpressionBuilder class is the factory for constructing new expressions.

== A Simple Expression Builder Expression ==

== A Simple Expression Builder Expression ==

This example uses the query key lastName to reference the field name L_NAME.

This example uses the query key lastName to reference the field name L_NAME.

The expression framework enables you to define complex queries at the object level. If your application requires a more complex query, use SQL or stored procedure calls to create custom database operations.

The expression framework enables you to define complex queries at the object level. If your application requires a more complex query, use SQL or stored procedure calls to create custom database operations.

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=== SQL Queries ===

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== SQL Queries ==

You can provide a SQL string to any query instead of an expression, but the SQL string must return all data required to build an instance of the queried class. The SQL string can be a complex SQL query or a stored procedure call. You can invoke SQL queries through the session read methods or through a read

You can provide a SQL string to any query instead of an expression, but the SQL string must return all data required to build an instance of the queried class. The SQL string can be a complex SQL query or a stored procedure call. You can invoke SQL queries through the session read methods or through a read

You can provide a StoredProcedureCall object to any query instead of an expression or SQL string, but the procedure must return all data required to build an instance of the class you query.

You can provide a StoredProcedureCall object to any query instead of an expression or SQL string, but the procedure must return all data required to build an instance of the class you query.

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=== A Read All Query With a Stored Procedure ===

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== A Read All Query With a Stored Procedure ==

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<code><pre>

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<source lang="java">

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ReadAllQuery readAllQuery = new ReadAllQuery();

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ReadAllQuery readAllQuery = new ReadAllQuery(Employee.class);

call = new StoredProcedureCall();

call = new StoredProcedureCall();

call.setProcedureName("Read_All_Employees");

call.setProcedureName("Read_All_Employees");

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call.useNamedCursorOutputAsResultSet("RESULT_CURSOR");

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readAllQuery.useNamedCursorOutputAsResultSet("RESULT_CURSOR");

readAllQuery.setCall(call);

readAllQuery.setCall(call);

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Vector employees = (Vector) session.executeQuery(readAllQuery);

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List employees = (List) session.executeQuery(readAllQuery);

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</pre></code>

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</source>

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== EJB QL ==

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= JPQL =

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EJB QL is a query language that is similar to SQL, but differs because it presents queries from an object model perspective and includes path expressions that enable navigation over the relationships defined for entity beans and dependent objects. Although EJB QL is usually associated with Enterprise JavaBeans (EJBs), EclipseLink enables you to use EJB QL with regular Java objects as well. In EclipseLink, EJB QL enables users to declare queries, using the attributes of each abstract entity bean in the object model. This offers the following advantages:

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JPQL (was EJBQL) is a query language that is similar to SQL, but differs because it presents queries from an object model perspective and includes path expressions that enable navigation over the relationships defined for entity beans and dependent objects. Although JPQL is usually associated with Enterprise JavaBeans (EJBs), EclipseLink enables you to use JPQL with regular Java objects as well. In EclipseLink, JPQL enables users to declare queries, using the attributes of each abstract entity bean in the object model. This offers the following advantages:

* You do not need to know the database structure (tables, fields).

* You do not need to know the database structure (tables, fields).

* You can use relationships in a query to provide navigation from attribute to

* You can use relationships in a query to provide navigation from attribute to

Line 83:

Line 83:

* You can construct queries using the attributes of the entity beans instead of

* You can construct queries using the attributes of the entity beans instead of

using database tables and fields.

using database tables and fields.

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* EJB QL queries are portable because they are database-independent.

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* JPQL queries are portable because they are database-independent.

* You can use SELECT to specify the query reference class (the class or entity

* You can use SELECT to specify the query reference class (the class or entity

bean you are querying against).

bean you are querying against).

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=== A Simple ReadAllQuery Using EJB QL ===

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== A Simple ReadAllQuery Using JPQL ==

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<code><pre>

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<source lang="java">

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ReadAllQuery theQuery = new ReadAllQuery();

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ReadAllQuery query = new ReadAllQuery(Employee.class);

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theQuery.setReferenceClass(EmployeeBean.class);

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query.setJPQLString("SELECT OBJECT(emp) FROM Employee emp");

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theQuery.setEJBQLString("SELECT OBJECT(emp) FROM EmployeeBean emp");

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…

…

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Vector returnedObjects = (Vector)aSession.executeQuery(theQuery);

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List employees = (List)session.executeQuery(query);

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</pre></code>

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</source>

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=== A Simple ReadAllQuery Using EJB QL and Passing Arguments ===

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== A Simple ReadAllQuery Using JPQL and Passing Arguments ==

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This example defines the query similarly to Example 6–30, but creates, fills, and passes a vector of arguments to the executeQuery method.

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This example defines the query similarly to above, but creates, fills, and passes a vector of arguments to the executeQuery method.

Query by example enables you to specify queries when you provide sample instances of the persistent objects to be queried.

Query by example enables you to specify queries when you provide sample instances of the persistent objects to be queried.

To define a query by example, provide a ReadObjectQuery or a ReadAllQuery with a sample persistent object instance and an optional query by example policy. The sample instance contains the data to query, and the query by example policy contains optional configuration settings, such as the operators to use and the attributes to consider or ignore.

To define a query by example, provide a ReadObjectQuery or a ReadAllQuery with a sample persistent object instance and an optional query by example policy. The sample instance contains the data to query, and the query by example policy contains optional configuration settings, such as the operators to use and the attributes to consider or ignore.

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=== Using Query by Example ===

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== Using Query by Example ==

This example queries the employee Bob Smith.

This example queries the employee Bob Smith.

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<code><pre>

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<source lang="java">

ReadObjectQuery query = new ReadObjectQuery();

ReadObjectQuery query = new ReadObjectQuery();

Employee employee = new Employee();

Employee employee = new Employee();

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Line 125:

query.setExampleObject(employee);

query.setExampleObject(employee);

Employee result = (Employee) session.executeQuery(query);

Employee result = (Employee) session.executeQuery(query);

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</pre></code>

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</source>

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=== Using Query by Example ===

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== Using Query by Example ==

This example queries across the employee’s address.

This example queries across the employee’s address.

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<code><pre>

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<source lang="java">

ReadAllQuery query = new ReadAllQuery();

ReadAllQuery query = new ReadAllQuery();

Employee employee = new Employee();

Employee employee = new Employee();

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employee.setAddress(address);

employee.setAddress(address);

query.setExampleObject(employee);

query.setExampleObject(employee);

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Vector results = (Vector) session.executeQuery(query);

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List results = (List) session.executeQuery(query);

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</pre></code>

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</source>

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=== Query by Example Policy Using Like ===

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== Query by Example Policy Using Like ==

This example uses like for Strings and includes only objects whose salary is greater than zero.

This example uses like for Strings and includes only objects whose salary is greater than zero.

Latest revision as of 16:20, 23 June 2008

Queries are the cornerstone of EclipseLink applications. Queries enable you to retrieve information or objects from the database, modify or delete those objects, and create new objects on the database.

Expressions

EclipseLink expressions enable you to specify query search criteria based on the object model. EclipseLink translates the resulting query into SQL and converts the results of the query into objects. EclipseLink provides two public classes to support expression:

The org.eclipse.persistence.expressions.Expression class represents an expression, which can be anything from a

simple constant to a complex clause with boolean logic. The developer can manipulate, group, and integrate expressions in several ways.

The org.eclipse.persistence.expressions.ExpressionBuilder class is the factory for constructing new expressions.

A Simple Expression Builder Expression

This example uses the query key lastName to reference the field name L_NAME.

An Expression Using the and() Method

Custom SQL

The expression framework enables you to define complex queries at the object level. If your application requires a more complex query, use SQL or stored procedure calls to create custom database operations.

SQL Queries

You can provide a SQL string to any query instead of an expression, but the SQL string must return all data required to build an instance of the queried class. The SQL string can be a complex SQL query or a stored procedure call. You can invoke SQL queries through the session read methods or through a read
query instance.

JPQL

JPQL (was EJBQL) is a query language that is similar to SQL, but differs because it presents queries from an object model perspective and includes path expressions that enable navigation over the relationships defined for entity beans and dependent objects. Although JPQL is usually associated with Enterprise JavaBeans (EJBs), EclipseLink enables you to use JPQL with regular Java objects as well. In EclipseLink, JPQL enables users to declare queries, using the attributes of each abstract entity bean in the object model. This offers the following advantages:

You do not need to know the database structure (tables, fields).

You can use relationships in a query to provide navigation from attribute to

attribute.

You can construct queries using the attributes of the entity beans instead of

using database tables and fields.

JPQL queries are portable because they are database-independent.

You can use SELECT to specify the query reference class (the class or entity

Query By Example

Query by example enables you to specify queries when you provide sample instances of the persistent objects to be queried.
To define a query by example, provide a ReadObjectQuery or a ReadAllQuery with a sample persistent object instance and an optional query by example policy. The sample instance contains the data to query, and the query by example policy contains optional configuration settings, such as the operators to use and the attributes to consider or ignore.